(1) The Field of the Invention
The invention refers to modacrylic fibres, viz. fibres consisting of copolymers of acrylonitrile with other comonomers copolymerizable therewith and wherein acrylonitrile is present in amounts from 50 to 85% inclusive, possessed of reduced inflammability, high gloss and high retraction, and to a process for their manufacture.
(2) The Prior Art
According to the standards of this art, fibers having a retraction of at least 35%, measured under the conditions hereinafter to be specified, are considered to be high retraction fibers.
Fibers of said type are desirable in particular for the manufacture of synthetic furs. Said manufacture requires the use of high retraction fibers also having adequate mechanical properties and a good glossiness; it is further highly desirable for this particular application that the fibre should have a reduced inflammability.
The problem of obtaining such fibers has not found a complete and satisfactory solution in the art up to now. As far as the Applicant knows, no modacrylic fiber having reduced inflammability and high retraction, suitable for the production of imitation furs, exists on the market.
Actually methods are known for producing high inflammability, high retraction modacrylic type fibers, but they involve manufacturing processes that are significantly more complicated than those employed for standard acrylic fibers. A process of this kind is described, e.g., in British Pat. No. 998,990, which describes the preparation of fibres from binary copolymers of acrylonitrile and, e.g. vinyl acetate, and mentions the possibility of making ternary copolymers of acrylonitrile, a vinylpyridine or vinylimidazole, and methacrylonitrile or vinyl chloride, or further, to use mixtures of binary interpolymers. In any case the said polymers do not have reduced inflammability, since to be considered as reduced inflammability fibers, the fibers must have a LOI index of at least 26.
In order to obtain a high retraction, a rather complicated process is adopted in said patent, which comprises the following steps:
(1) After coagulation, the fibers undergo a reduced stretch, to a draw ratio from 1.5 to 2.5 (instead of the 5-6 draw ratios which are customary for standard acrylic fibers) in a boiling water bath and a subsequent washing and a finishing with suitable antistatic and lubricating agents; PA1 (2) After the finishing, the fibers are dried on calendering rolls internally heated to 120.degree. C.; PA1 (3) The fibers are caused to contract freely by treatment with saturated steam at a pressure from 35 to 55 psi; PA1 (4) After contraction, the fibers undergo a second stretch to draw ratios from 1.3 to 3, in a water bath kept between 70.degree. and 95.degree. C.; PA1 (5) The fibers are then cooled while being maintained under sufficient tension to prevent them from shrinking; and PA1 (6) The fibers are subjected to a second drying effected under tension by means of air at a temperature below 70.degree. C. PA1 (a) The drawing in water is effected at a temperature from 80.degree. to 100.degree. C. PA1 (b) The drying in air is effected at temperatures between 110.degree. and 120.degree. C. PA1 (c) The hot drawing in air is effected at temperatures between 70.degree. and 80.degree. C. PA1 (a) two copolymers are separately prepared, preferably by copolymerization in the spinning solvent, which have the following preferred compositions: the first, a binary copolymer, is constituted by acrylonitrile and the monomer containing at least a sulphonic group, and in it, the acrylonitrile content varies from 63 to 92% by weight and the sulphonic monomer content varies from 37 to 8% by weight; and the other is a ternary copolymer constituted by acrylonitrile, vinylidene chloride and vinyl ester, wherein the acrylonitrile content is from 32 to 76% by weight, the vinylidene chloride content from 20 to 57% by weight, and the vinyl ester content from 4 to 11% by weight; and the solutions of the two copolymers in the same spinning solvent are mixed in such proportions that the resulting copolymer mixture will have the following preferred composition by weight: units deriving from acrylonitrile from 50 to 85%, units deriving from vinylidene chloride from 10.5 to 40.5%, units deriving from the monomer containing at least a sulphonic group from 1.5 to 3.5% and units deriving from the vinyl ester from 3 to 6%; or optionally PA1 (b) the binary copolymer is prepared as indicated at (a) by a first copolymerization in solution in the spinning solvent, the resulting solution (A) is added to a solution (B) of the comonomers of the ternary copolymer hereinbefore defined, and the whole is subjected to a second copolymerization, the amount of solution (A) added being such that the resulting final polymeric material will have the following preferred composition by weight: units deriving from acrylonitrile from 50 to 85% units deriving from vinylidene chloride from 10.5 to 40.5%, units deriving from the monomer containing at least a sulphonic group from 1.5 to 3.5%, and units deriving from the vinyl ester from 3 to 6%.
It is obvious that this is a rather complicated discontinuous treatment which requires extremely long times and therefore very large and expensive driers, since the final drying has to take place at rather low temperatures. Therefore the treatment considerably raises the production cost of the fiber.
The known art does not disclose any simpler systems for producing high retraction acrylic and modacrylic fibers, and the making of such fibers with low inflammability is not even considered in the known processes, at least not with respect to LOI index values of at least 26.
It is clear that it would be highly desirable to provide a process for the preparation of a copolymer adapted for the manufacture of fibers possessed of high retraction, reduced inflammability, high gloss, and adequate mechanical characteristics, simple enough to be carried out in the installations generally used for the manufacture of standard acrylic and modacrylic fibers.